GSuite Signature sync - Unifies signatures of all users by copying the signature of the selected user.

signature.js

const {google} = require('googleapis');
const {JWT} = require('google-auth-library');

const MasterUser = "adam.dobrawy@siecobywatelska.pl";
const OrganizationDomain = 'siecobywatelska.pl';

function getAuthClient(options) {
    const authClient = new JWT(Object.assign({}, {
        email: 'vacationreplymanager@vacationreplymanager.iam.gserviceaccount.com',
        keyFile: 'keys/vacationreplymanager-7dbf49809e60.json',
    }, options));
    authClient.authorize();
    return authClient;
}

function getGmailClient(user) {
    const authClient = getAuthClient({
        subject: user,
        scopes: [
            'https://mail.google.com/',
            'https://www.googleapis.com/auth/gmail.settings.sharing',
            'https://www.googleapis.com/auth/gmail.settings.basic'
        ]
    });
    return google.gmail({
        version: 'v1',
        auth: authClient
    });
}

const getDirectoryClient = user => {
    const authClient = getAuthClient({
        subject: user,
        scopes: [
            'https://www.googleapis.com/auth/admin.directory.user.readonly',
        ]
    });
    return google.admin({version: 'directory_v1', auth: authClient})
};

const getUsers = async () => {
    const directory = getDirectoryClient(MasterUser);
    return directory.users.list({
        domain: OrganizationDomain
    }).then(resp => resp.data.users.map(user => user.primaryEmail))
};

const getSignature = async () => {
    const gmail = getGmailClient(MasterUser);
    const resp = await gmail.users.settings.sendAs.list({
        userId: 'me'
    });
    return resp.data.sendAs.find(x => x.signature).signature;
};

const updateSignature = (gmail, signature, user) => async sendAs => gmail.users.settings.sendAs.patch({
    userId: 'me',
    sendAsEmail: sendAs.sendAsEmail,
    requestBody: {
        signature: signature
    }
}).then(() => console.log(`Updated signature at ${sendAs.sendAsEmail} of ${user}.`));

const updateUser = signature => async user => {
    const gmail = getGmailClient(user);
    const resp_list = await gmail.users.settings.sendAs.list({
        userId: 'me'
    });
    const needUpdate = resp_list.data.sendAs
        .filter(sendAs => sendAs.signature !== signature);
    console.log(`${needUpdate.length} emails of ${user} need update`);
    await Promise.all(needUpdate.map(updateSignature(gmail, signature, user)));
};

const main = async () => {
    const signature = await getSignature();
    console.log(`Signature length ${signature.length} available.`);
    const users = await getUsers();
    console.log(`${users.length} users founds.`);
    await Promise.all(users.map(updateUser(signature)));
};

main().catch(err => {
    console.log("Something happened", err);
});